One of the major problems with electronic commerce such as over the Internet is that there is currently no way to sign electronically a document which is comparable in security, strength, ease of use, and user preparation to the traditional handwritten signature on a paper document. An effective electronic signature involves three components. First, there must be effective binding of the signature to the individual (signer). Second, there must be effective binding of the signature to the document. Finally, there has to be some way of ensuring that the signature is in some way unique so that it cannot be copied and employed by other parties attempting to pretend to be the signer. This aspect is referred to as “resistance to replay.”
The most common form of electronic signing involves appending a personal identification number (PIN) to a document. This approach is effective only if the PIN is known only to the signer and the receiver and some mechanism is employed to prevent or detect interception of the PIN. Depending upon the implementation, this approach may or may not indicate whether the document has been altered since “signing.” The existing state of the art for electronic signing employs public key infrastructure (PKI). In PKI, a polynomial-based hash of the document to be signed is generated. The hash is then encrypted based on the signer's private key. The signed document is sent to the receiver, who uses the signer's public key to decrypt the hash and then revalidate the hash. Successful revalidation indicates that the document has not changed since signing. This approach assumes that the signer protects his/her private key so that anything encrypted by the private key is assumed to be signed by him or her.
The PKI technique has disadvantages, however. For PKI to work, an infrastructure must be in place to generate and distribute a public/private key pair to every signer. This infrastructure is costly to set-up and maintain. The key pair has to be securely distributed to the signer in advance of signing. To clearly and uniquely associate the signer with the key pair, this distribution is usually done through some face-to-face process. In addition, the signer must ensure that the private key is not ever in the possession of any third party.
It is therefore desirable to have an electronic signature system that creates a signature that is strongly bound to the user and strongly bound to the document but not requiring the issuance of private/public keys to each signer.